Add example query for nr of comments by class.

WHERE target.domain = ?

GROUP BY target.id

-- get number of comments for each class (including comments for class members)

SELECT

    target.cls AS cls,

    count(*) AS cnt

FROM comments JOIN targets ON comments.target_id = targets.id

WHERE target.domain = ? AND target.type = 'class'

GROUP BY target.cls

-- get users with the highest score

SELECT